A problem related to radio receivers in small wireless communication devices is that the radio frequency (RF) components need to be miniaturized. However, miniaturization of RF components will typically result in RF components that have reduced performance, in terms of noise and RF interference performance etc., than RF components that are not miniaturized, for example components that are used in products such as radio base stations. Furthermore, RF components need to be cost effective and power efficient which sets additional performance challenges. Hence, in order to enable use of such reduced performance RF components while still maintaining good radio performance in radio receivers, improved interference cancellation is needed.
As will be illustrated in more detail below, sensitivity in a receiver (RX) chain in a node that comprises also a transmitter (TX) chain may be degraded due to so-called crosstalk between the TX chain and the RX chain. In the context of the present disclosure, crosstalk comprises limited TX-RX isolation in a duplex filter or direct coupling from TX to RX or due to spurious frequencies generated by passive and/or active intermodulation in the RF components, which may fall within the RX own frequency band and thus degrading the RX sensitivity. The degradation of the RX sensitivity may be severe, for example in some frequency bands it may be larger than 10 dB.
In the prior art, attempts have been made to overcome such drawbacks. For example, in Transmit and Receive Crosstalk Cancellation by authors Amin and Weber, 978-1-4244 -8058-6/10/$26.00 ©2010 IEEE 2010 6th International Conference on Emerging Technologies (ICET) pages 210-215 attempts are made to cancel crosstalk by using two feedback paths from a TX chain; one path provides feedback to a pre-distortion process and a second path provides feedback for cancelling intermodulation interference.
Furthermore, U.S. patent application publication US 2012/0295558 describes crosstalk cancellation and dynamic cancellation of passive intermodulation interference. The method presented in US 2012/0295558 requires a test signal that originates from a test signal transmitter.